Large-aperture photographic lens with seven elements in five groups

ABSTRACT

A large-aperture photographic lens adapted for use as the standard lens with single-lens reflex cameras. The lens consists of seven elements in five groups and has a back focal length greater than 0.68 times the focal length of 1.0 a picture angle of 44* and an f-number of 1.1. The image errors, especially the spherical aberration of the higher order, are well corrected.

I mm OR 3,617,111 5V I r Umtea Dlfllta 3,617,111

[ 72] Inventor Motoaki Kawazu [56] References Cited Java UNITED STATESPATENTS g gg' 2353 1970 2,735,339 2/1956 D01 350/217 [45] Patented Nov.2,1971 2,959,103 11/1960 Cook 350/217 X [73] Assignee Ricoh Co., Ltd.Primary Examiner-John K. Corbin Tokyo, Japan Attorneys-Henry T. Burke,Robert Scobey, Robert S. [32] Priority Aug. 28, 1969 Dunham, P. E.Henninger, Lester W. Clark, Gerald W. [33] Japan Griffin, Thomas F.Moran, R. Bradlee Boal and Christopher [31] 44/67584 C. Dunharn [54]LARGE-APERTURE PHOTOGRAPHIC LENS WITH SEVEN ELEMENTS IN FIVE GROUPS 1Claim, 4 Drawing Figs. ABSTRACT: A large-aperture photographic lensadapted for use as the standard lens with single-lens reflex cameras.The

[52] US. Cl 350/217, lens consists of seven elements in five groups andhas a back 350/176 focal length greater than 0.68 times the focal lengthof 1.0 a [51] Int. Cl G02b 9/60 picture angle of 44 and an f-number of1.1. The image errors, [50] Field of Search 350/217, especially thespherical aberration of the higher order. are

176 well corrected.

PATENTED 2 3,617, l l l FIG. 28 FIG. 2C

- 000|a 0 0.00|e -0.0036 0 00018 4 0 73; I

SPHERICAL DISTORTION ABERRATION ASTIGMATISMI MOTOAK! KAwAzu INVENTOR.

A TTO RUE) LARGE-APERTURE PHOTOGRAPHIC LENS WITH SEVEN ELEMENTS IN FIVEGROUPS BACKGROUND OF THE INVENTION The present invention relates to aphotographic objective and more particularly a large-aperturephotographic objective which may be used as a standard lens forsingle-lens reflex cameras and has a back focal length greater than 0.68times the focal length, a picture angle of 44 and an f-number of 1.1.

It is impossible to employ a lens having a back focal length shorterthan a predetermined length with a single-lens reflex camera whose imagespace is occupied by a hinged mirror. Furthermore, it is very difficultto provide a large-aperture standard photographic objective having alonger back focal length especially because the outer diameter of therear lens group of a lens system is limited by a lens mount having apredetermined diameter.

SUMMARY OF THE INVENTION It is therefore the primary object of thepresent invention to provide a large-aperture photographic objectivelens consisting of seven lenses in five groups which can eliminate theabove-described defects and whose image errors, especially the sphericalaberration of the higher order, are well corrected so that the bulgingof the aberration curve which tends to occur especially in case of alarge-aperture lens, the furrows which tend to occur along theperipheral edge and the coma may be sufficiently eliminated. Theinvention will become more apparent from the following description ofthe preferred embodiment thereof taken in conjunction with theaccompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. I is a diagrammatic view of oneembodiment of the present invention; and

FIG. 2A depicts the spherical aberration curve, FIG. 2B, the astigmatismcurve and FIG. 2C, the distortion curve.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, alarge-aperture photographic lens in accordance with the presentinvention comprises seven elements divided into five groups. Moreparticularly, the largeaperture photographic objective of the presentinvention is a modification of the so-called Gauss objective, in whichthe rear group is further divided into two groups or elements. The firstgroup (the groups or elements being numbered from front to rear) Iconsists of a positive meniscus lens; the second group 11 consists ofthe second positive meniscus lens 2 and third negative meniscus lens 3cemented together; the third group 111 consists of a biconcave lens 4and a biconvex lens 5 cemented together; the fourth group IV consists ofa positive meniscus lens 6; and the fifth group V consists of a biconvexlens 7. A stop 8 is interposed between the third lens 3 and fourth lens4.

The design data are given below, where r with a subscript designates aradius of curvature of a surface identified by the subscript, thesurfaces being numbered from front to rear and a positive radiusindicating a surface convex toward the front while a minus radiusindicates a surface concave toward the front;

d with a subscript designates a thickness of a lens or a distance ofairspace along the optical axis identified by the subscript. thethicknesses and distances of airspace being numbered from front to rear;with a subscript designates an index of refraction when using d-line ofhelium of a lens identified by the subscript; and v with a subscriptdesignates a dispersion ratio of a lens Spherical Astlgaberration Comamatism Curvature Distortion 1 0, 441 0. 083 0. 016 0. 541 0. 0. 039 0.149 0. 568 0. 171 -l.. 523 0. 024 0. 009 -0. 003 0. 831 0. 315 0.007 0.017 0. 041 O. 013 0. 065 -0. 795 0. 259 0. 085 1.337 0. 464 1. 742 0.720 0. 298 -1. 280 0. 652 0. 009 0. 016 0. 028 0. 002 0. 052 0. 350 0.147 0. 060 0. 778 0. 344 0. 003 0. 015 0. 071 0. 154 1. 043 1. 323 0.023 0.000 0. 6'29 0. 011 0. 002 0. 027 0. 340 0. 290 u. 633 0. 604 0.249 0. 123 0. 0'12 0. 071

The aberration curves are shown in FIG. 2 in which the curves d, g and cdesignate the spherical aberration curves for d-line of helium, g-lineof mercury and c-line of hydrogen while the curves M and S designate(the astigmatism curves) in the meridional and sagittal planesrespectively.

It will be seen that the spherical aberration at higher orders is wellcorrected and the flare at full aperture may be minimized. Furthermore,the coma and astigmatism are also well corrected as seen from the Seidelcoefficients, so that an object may be sharply imaged.

Iclaim:

1. A large-aperture photographic objective consisting of seven elementsin five groups, which are numbered from front to rear; the first groupconsisting of a positive meniscus lens; the second group consisting ofpositive meniscus and negative meniscus lenses cemented together; thethird group consisting of a biconcave and biconvex lenses cementedtogether; the fourth group consisting of a positive meniscus lens; andthe fifth group consisting ofa biconvex lens; and satisfying thefollowing conditions:

Bf=0.6825 f where r with a subscript designates a radius of curvature ofa surface of a lens identified by the subscript, the surface beingnumbered from front to rear and a positive radius indicating a surfaceconvex toward the front while a minus radius, a surface concave towardthe front;

at with a subscript designates a thickness of a lens or distance ofairspace along the optical axis identified by the subscript, thethicknesses and distances being numbered from front to rear;

n with a subscript designates an index of refraction of a lensidentified by the subscript when d-line of helium is used;

V with a subscript designates a dispersion ratio of a lens identified bythe subscript;

f= compound focal length; 5

Bf= back focus;

F =f-number; and

2 w total field of view.

1. A large-aperture photographic objective consisting of seven elementsin five groups, which are numbered from front to rear; the first groupconsisting of a positive meniscus lens; the second group consisting ofpositive meniscus and negative meniscus lenses cemented together; thethird group consisting of a biconcave and biconvex lenses cementedtogether; the fourth group consisting of a positive meniscus lens; andthe fifth group consisting of a biconvex lens; and satisfying thefollowing conditions: f 1.0 Bf 0.6825f F 1.1 2 omega 44* r1 0.82451 d10.11203 n1 1.80440 V1 39.6 r2 2.61302 d2 0.00181 r3 0.51829 d3 0.13191n2 1.75700 V2 47.8 r4 0.99758 d4 0.05782 n3 1.71736 V3 29.5 r5 0.31233d5 0.33971 r6 -0.34345 d6 0.02710 n4 1.78472 V4 25.6 r7 3.26154 d70.19154 n5 1.76200 V5 40.2 r8 -0.55605 d8 0.00181 r9 -2.71114 d9 0.12107n6 1.71300 V6 53.9 r10 -0.66134 d10 0.00181 r11 1.45848 d11 0.06324 n71.77390 V7 50 r12 -19.87641 where r with a subscript designates a radiusof curvature of a surface of a lens identified by the subscript, thesurface being numbered from front to rear and a positive radiusindicating a surface convex toward the front while a minus radius, asurface concave toward the front; d with a subscript designates athickness of a lens or distance of airspace along the optical axisidentified by the subscript, the thicknesses and distances beingnumbered from front to rear; n with a subscript designates an index ofrefraction of a lens identified by the subscript when d-line of heliumis used; V with a subscript designates a dispersion ratio of a lensidentified by the subscript; f compound focal length; Bf back focus; Ff-number; and 2 omega total field of view.